Control element for electrical reading or recording device

ABSTRACT

This invention relates to an element for controlling the reading or recording of information with an electrically controlled device. The element includes a track having a normal pattern of sync markings spaced from each other by a predetermined distance and at least one area having a sync pattern differing from the normal pattern. The area having a different sync pattern may not have a marking appear within a predetermined distance of a given marking or may have a distance different from said predetermined distance between selected ones of the markings. All of the sync markings on the track are scanned during the reading or recording of each line of information characters and are utilized for generating sync pulses which control the reading or recording of a stroke of an information character. The variable spacing of the sync markings on the sync track may be utilized to vary the size of the characters recorded, to justify characters of different size, to protect selected areas of the media being recorded on, to encode the information, or for other control purposes.

United States Patent Boyce et al.

[ 1 Sept. 16, 1975 1 1 CONTROL ELEMENT FOR ELECTRICAL READING ORRECORDING DEVICE [75) Inventors: James J. Boyce, Fresh Meadows,

N.Y.', Angelo .1. Di Giugno, Norwalk; James V. Masi, Monroe, both ofConn.

{73] Assignee: The Bunker Ramo Corporation, Oak

Brook, 111.

[22] Filed: Feb. 12, 1973 [211 Appl. No.: 331,838

[52] US. Cl. 197/1 R; 197/84 B [51] Int. Cl B41] 3/05 [58] Field ofSearch 197/1 R, 18, 19, 20, 84 B, 197/84 R, 176; 101/93 C [56[References Cited UNITED STATES PATENTS 2,701,632 2/1955 Zint 197/84 R2,847,919 8/1958 Rossetto et al. 197/19 X 2.997.152 8/1961 Dirks 197/19X 3,006,259 10/1961 Blakely... 197/19 X 3.061537 11/1962 Allen 1111111197/176 X 3,464,349 9/1969 Ritzerfeld [97/19 X 3,528,063 9/1970 Kolpek197/19 X 3,614,394 10/1971 Bindshedler... 197/1 UX 3,690,431 9/1972Howard 197/1 R Primary ExaminerEdgar S. Burr Assistant ExaminerR. T.Rader Attorney, Agent, or FirmD. R. Bair; F. M. Arbuckle 1 1 ABSTRACTThis invention relates to an element for controlling the reading orrecording of information with an electrically controlled device. Theelement includes a track having a normal pattern of sync markings spacedfrom each other by a predetermined distance and at least one area havinga sync pattern differing from the normal pattern. The area having adifferent sync pattern may not have a marking appear within apredetermined distance of a given marking or may have a dis taneedifferent from said predetermined distance between selected ones of themarkings. All of the sync markings on the track are scanned during thereading or recording of each line of information characters and areutilized for generating sync pulses which control the reading orrecording of a stroke of an informa tion character. The variable spacingof the sync mark ings on the sync track may be utilized to vary the sizeof the characters recorded, to justify characters of different size, toprotect selected areas of the media being recorded on, to encode theinformation, or for other control purposes.

8 Claims, 12 Drawing Figures PATENTEB 3,905,463

CRlF CONT R01.

CONTROL ELEMENT FOR ELECTRICAL READING OR RECORDING DEVICE Thisinvention relates to an element for controlling the reading or recordingof information with an electrically controlled device, and moreparticularly, to an element of this type utilizing a special sync trackhaving variably spaced markings formed thereon.

BACKGROUND OF THE INVENTTON All printers, magnetic recorders, and otherelectronically controlled devices for recording information, and alloptical readers, magnetic detectors, and other electrically controlleddevices for reading recorded information have one thing in common; thereading or recording is accomplished by either moving a readrecordelement relative to a stationary medium or by moving the medium relativeto a stationary read-record element. While the speed at which theelement and the medium move relative to each other may vary, it isnormally required that information always be recorded at the same spoton the medium and that it be read from the same spots. In order toassure this synchronization, a sync track is generally provided which isassociated with the medium, reading or recording of a bit of informationon the medium being permitted only when the element and the medium arealigned so that a mark on the sync track is being read.

An example of a printer utilizing a sync track of the type describedabove is found in U.S. Pat. No. 3,690,431 entitled Print Head AssemblyContaining Solenoids issued Sept. 12, 1972 to Robert Howard and assignedto Centronics Data Computer Corp. With this printer, characters arerepresented by selectively impregnating dots in a 5 X7 character matrix.The paper which is being printed on is held stationary in a carriagewhich has a sync track associated with it, printing being accomplishedby a moving wire print head, which head has the wires for printing asingle seven bit stroke or column of the character each time it isenergized. A light source and/or detector photocell are positioned onopposite sides of the optical sync track and move with the print head.An output is obtained from the detector when it is adjacent a sync markon the track and is applied to enable the print head. Thus, printingoccurs at the same spots and with the same spacing between print strokesregardless of the speed at which the print head moves.

However, the system described above does have limitations in certainspecial situations. First since a 5X7 matrix is utilized for generatingall characters, a period takes up the same space as a letter such as aw. The printer thus does not have the ability to justify for charactersize even when it is known that a punctuation mark or some other one ortwo stroke character will always appear in a particular characterposition. One place where this can be a particular problem is whenprinting numbers, where a period is being utilized as a decimal point.Here, an extra space before or after the period of the decimal point isaesthetically undesirable.

Another limitation of the existing sync system is that all printedcharacters are of the same size. There are special situations where itmay be desired to print characters of different size on the same linesuch as, for example, to distinguish between dollars and cents on a lineof text or to emphasize or call attention to special items. Also, thesame print head may be utilized to print on different mediums such as,for example, a bank pass book and a journal during a single line ofprinting. Because of differences in the size of the medium or the use towhich it is to be put, it may be desired for the print to be larger onone of these mediums and smaller on the other. Another possiblesituation where it might be desired to print characters of two differentsizes during a single line of printing would be where two writing headswere provided, one providing a visual printing and the other, forexample, recording information magnetically on a selected area of themedium. Particularly in the latter situation where information is beingrecorded magnetically or in some other way which is not visible to thehuman eye, it might be desirable to provide random spacing of the writestrokes so that only a device having the same random spacing on its synctrack may be utilized to read the material. A relatively simple,substantially tampered-proof system is thus provided for recording forexample an account balance to permit off-line banking. Such a codingarrangement could also be utilized in other similar applications.

In order to provide the various capabilities indicated above, arequirement exists for permitting variable spacing between the read orrecord strokes for different characters on a line, or even between thestrokes of a given character of the line. Existing synchronizationsystems do not provide such a capability. While certain prior artsynchronization systems have provided several sync tracks for permittingprinting of different size characters, only one of these sync tracks isutilized for printing a given line and all characters on the given lineare of the same size. A synchronization system for premitting theprinting of the characters of different size on a single line is thusrequired.

In addition to providing variable sized characters on a single line, aflexible sync system might also be utilized for solving other problems.For example, with a printer of the type described above, the print headis normally accelerating at the beginning of the line and deceleratingat the end of the line. The head is thus moving somewhat slower at thebeginning and end of the line than on the remainder of the line. Withthe head continuously moving, there is a slight offset between theinstant that a print command is received (i.e. a sync mark is detected)and the time the print solenoids in the print head are actuallyenergized to cause a print operation to be performed. This offset isgreater when the head is moving faster than it is when the head ismoving slower. By suitable adjustment within the sync system, thisoffset difierential could be eliminated.

The offset problem is even more serious when the printer is beingutilized in a manner such that it prints from left to right during oneline and from right to left during the succeeding line. Such a mode ofoperation is desirable in very high speed printers since it eliminatesthe delay time otherwise required for print head flyback. [t is apparentthat with this mode of operation, if the same sync marks are utilized,there will be a slight offset to the right of the sync marks during aleft-toright print line and a slight offset to the left of the sync markduring a right-to-left print line. The combined effects of these offsetscould result in a noticeable mis alignment of the two lines. Again, arequirement exists for providing a means within the sync system tocompensate for these offsets.

Further, where the document to be printed on does not completely fillthe carriage, it is important, in order to prevent damage to thecarriage, that printing only occur in the areas where the document ispositioned. Also, on a given document, there may be areas which containinformation, either visible or invisible, which is to be protectedagainst overwriting. Again. it would be desirable if the sync systemcould be provided with a capability for performing this function.Finally. the sync system might also be utilized for controlling theperformance of certain logic functions, in particular such functions astabbing or carriage return line feed.

SUMMARY OF INVENTION In accordance with the above this inventionprovides a control element for use in an electrically controlled devicefor reading or recording lines of information characters, each of whichcharacters are formed from a selected plurality of strokes. The controlelement includes a track having a normal pattern of sync markings spacedfrom each other by a predetermined distance and at least one area havinga sync pattern differing from the normal pattern. The area having adifierent sync pattern may not have a new marking appear within thepredetermined distance of a given marking or may have a distancedifferent from said predetermined distance between selected ones of themarkings. The element also includes a means operative during the readingor recording of each line of information characters for detecting allthe sync markings of both the normal pattern and the pattern in the atleast one area, the detecting means including a means responsive to eachdetected marking for generating a sync pulse. Finally, the controlelement includes a means responsive to each of the sync pulses forcontrolling the reading or recording of a single stroke of aninformation character.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. I is a perspective view of a printerof the type in which the control element of this invention might beutilized.

FIG. 2A is an illustration of the type of documents on which printingmight be performed utilizing the teachings of this invention as theymight be mounted in a printer of the type shown in FIG. 1.

FIG. 2B is a character number chart and a chart of the relative positionof the documents on the printer carriage.

FIG. 2C is a perspective view of a sync track suitable for use with adocument arrangement as shown in FIG.

FIG. 3A is a perspective view of a sync track for an illustrativeembodiment of the invention.

FIG. 3B is an illustration of illustrative characters obtained utilizingthe sync track of FIG. 3A.

FIG. 4A is a perspective view of a sync track for another illustrativeembodiment of the invention.

FIG. 4B is a diagram illustrating a few illustrative characters recordedutilizing the sync track of FIG. 4A.

FIGS. 5, 6 and 7 are perspective views of sync tracks utilized for threeadditional alternative embodiments of the invention.

FIG. 8 is a semi-block schematic diagram of a control circuit suitablefor use with the embodiment of the invention shown in FIG. 7.

DETAILED DESCRIPTION Referring now to FIG. 1, a printer 8 of the typeshown in the beforementioned Howard patent is illustrated. This printerconsists of a carriage or platen 10 on which is mounted a document I2 tobe printed on. Samples of documents suitable for use as a documnt 12will be described later. A print head, for example a wire print head ofthe type shown in the beforementioned Howard patent, is mounted to bemoved across document 12 by a drive belt 16. Belt I6 is driven by amotor 18 under control of a print and carriage control mechanism 20.Except as specifically indicated later in the application, the natureand function of mechanism 20 are the same as for existing printers anddo not form part of the present invention. This mechanism will thereforenot be described further.

An optical sync track 22 is attached to the printer in a positionparallel to carriage 10. Track 22 is normally opaque but has spacedtransparent areas, each of which serves as a sync mark 23. A housing 24containing a light source 26 and a photocell 28 is mounted for movementwith print head 14. Housing 24 is U-shaped so that the light source andphotocell are on opposite sides of track 22. Thus, detector 28 isenergized to generate a sync pulse on line 30 each time housing 20 comesadjacent to a sync marking on track 22. The signal on line 30 is appliedto print head 14 to enable the head to print a single stroke of acharacter. Whether printing actually occurs when a signal appears online 30 and the number of wires which are energized to print aredetermined by other inputs to the print head which do not form part ofthe present invention. For reasons which will be described in greaterdetail later, sync pulse line 30 may also be connected as an input toprint and carriage control mechanism 20.

FIG. 2A illustrates in some detail documents of the type which may beprinted on printer 8 where the printer is being utilized as part of abank teller terminal. For this embodiment of the invention, an entry ismade both in a bank passbook 34 and a journal tape 38 dur ing a singleprint line, the information printed in the book and journal taperepresenting the same transaction. For this example, it is assumed thatthere are 145 possible character positions for the carriage. The bankpassbook 34 is positioned starting at character position 20 (FIG. 28) sothat there is a nonprintable margin in the area 40 'to the left of thepassbook. Positions 20 through 79 contain the bank passbook with a tencharacter space 42 being provided between the passbook and the journal.Positions through contain the journal tape, leaving a 20 characternonprintable right margin area 44. One each of the documents, there area number of fields or columns with the nature of the information to beprinted in each of these fields or columns being fixed. Thus, the firstcolumn of the passbook contains the date which could be a fixed two orthree alphabetic characters for the month, two numeric characters forthe day, a comma, and two numeric characters for the year. The nextcolumn is for withdrawals and would contain positions for four to fivenumeric characters for the dollars, a position for a period, and twonumeric positions for the cents. The information to be printed in theremaining columns of the passbook and in the various columns of thejournal tape are similarly fixed in format.

With the arrangement shown in FIGS. 2A and 28, it is apparent thatprinting is not to occur in the areas 40, 42 and 44 which do not containdocuments. Since print head 14 is not enabled unless a sync signalappears on line 30, protection against printing in these areas may beobtained by utilizing the sync track 46 shown in FIG. 2C in place of thestandard sync track 22. It is noted that with this sync track, there areareas 48, 50 and 52 which do not contain sync markings, the areas 48, 50and 52 corresponding to the nonprintable areas 40, 42 and 44respectively. The absence of sync markings in the areas 48, S0 and 52assures against the inadvertent energizing of print head I4 when it isadjacent to areas where printing might cause damage to the carriage 10,the print head, or both. The same technique could be utilized to protectagainst printing in a preprinted or otherwise to be protected field on adocument. For ex ample, the left-most field of the passbook is shown ascontaining preprinted line numbers. Sync pulses could be omitted in thearea of the sync track 46 corresponding to this field, protectingagainst the overwriting of these line numbers.

The predetermined format of the documents to be printed on with theembodiment ofthe invention shown in FIG. 2 permits other specializedfunctions to be performed. For example, the print density for allcharacters on both the passbook and the journal would normally be thesame, for example 12 characters per inch. However, as shown in FIG. 38,it might be desired to distinguish between dollars and cents in, forexample, the withdrawal, deposit, dividend, and/or balance columns ofthe passbook document by utilizing a smaller character for the centsthan is used for the dollars. Thus, for example, the print density forthe cents character might be 24 to the inch rather than 12 to the inch.As shown in FIGS. 3A and 313, this is accomplished by spacing the syncmarkings for the character positions in which the cents are to beprinted more closely together than are the sync markings for the othercolurnns.

Also, while five strokes are provided for each character, only two ofthese strokes are required for printing the period between the dollarsand cents. This results in there normally being an excessively large,and not aesthetically pleasing, space between the period and thebeginning of the cents indication. Particularly where there is a spaceproblem on the document, this problem may be solved, as shown in FIGS.3A and 38, by providing normal spacing for the sync markings for thefirst two strokes of the character which is to be a period, and spacingthe remaining three strokes of this character, and possibly the twostrokes for the intercharacter spacing, very closely together. This sametechnique could be utilized in other situations where justification ofpredetermined characters is desired. It is noted that in FIG. 3A thesync marks for the intercharacter spacings and the three unused syncmarks for the period have been shown dotted. As discussed previously,these sync marks may, if desired, be omitted to assure that data is notinadvertently printed in these positions.

FIG. 4 illustrates another situation in which variable spacing betweenthe sync markings might be utilized. Assume, for example, that inadditon to printing the passbook balance in a visual form, the balanceis also printed either magnetically with a suitable head, or in someother nonvisual form, and that the balance in nonvisual form is read bya suitable device and utilized to permit, for example, off-line banking.To prevent tampering with this non-visual material, it may be recordedwith random spacing between the strokes of the characters, a sync track56 such as that shown in FIG. 4A being utilized for this purpose. Theappearance of the resulting characters is shown in FIG. 4B. A similartechnique could be utilized for the secure recording of magnetic dots orlines or for recording information in any other form.

As indicated previously, there is a slight disparity in off-set when aprint head is moving slowly during acceleration and deceleration thenwhen the print head is moving at normal speed. FIG. 5 shows a sync track58 which may be utilized to compensate for this disparity in off-set. Asseen in this figure, the sync markings 23 at the beginning and end ofthe track are spaced somewhat closer together (the difference in spacingbeing exaggerated for purposes of illustration) than the spacing at thecenter of the track.

FIG. 6 illustrates a sync track 60 which may be utilized to compensatefor the off-set problem which arises when a print head prints both whenmoving from left to right and from right to left. The sync markings 62on this track are slightly wider than normal (two closely spaced syncmarkings may also be utilized). If a snyc pulse is generated on line 30when the leading edge of a sync mark 62 is detected, and the width ofthe mark 62 is roughly equal to twice the normal print off set, thenprinting will always occur at the same position on the line, alignedwith roughly the middle of the sync mark, regardless of the direction inwhich the print head is moving.

FIGS. 7 and 8 illustrate another application to which the teachings ofthis invention may be applied. In FIG. 7, a standard sync track 22 isshown with a slideable shutter 64 position on its right end. Inapplications where a variable right margin is to be provided, shutter 64is moved to a position on sync track 22 corresponding to the desiredright margin on the document. When housing 24 reaches this point on thesync track, sync pulses no longer appear on line 30. Referring to FIG.8, it is seen that mechanism 20 contains, among other circuitry, asingle-shot which is set by a sync pulse on line 30 and reset togenerate an output on line 72 if it does not receive another sync pulseon line 30 within a predetermined period of time equal to, for example,three or four sync pulse intervals. Assume initially that a carriagereturn line feed signal appears on line 74, causing flip flop 76 to bereset to its ZERO state. When print head 14 starts moving again anddetector 28 detects the first sync marking 23 on track 22, a signalappears on line 30 setting single-shot 70 and also applying an inputsignal to AND gate 78. Since flip flop 76 i in its ZERO state at thistime, AND gate 78 is fully conditioned to generate an output which setsflip flop 76 to its ONE state. Flip flop 76 being in its ONE stateresults in an output on its one-side output line 80 which signal isapplied as one input to AND gate 82. So long as successive sync markingsare being detected on track 22, single-shot 70 remains set and there isno output on line 72. However, when housing 24 reaches shutter 64, syncpulses are no longer detected and single shot 72 times out, resulting ina signal on line 72 which fully conditions AND gate 82 to generate acarriage return line feed control signal on line 74. The signal on line74 resets flip flop 76 to its ZERO state, inhibiting the generation ofadditional carriage return line feed control signals until the printingof a new line has commenced.

It is apparent that a circuit such as that shown in FIG. 8 could also beutilized for other control functions such as for tabbing or the like. Itis also apparent that the applications indicated above for usingdifferent sized characters are by way of illustration only, and thatsync tracks having variably spaced sync markings might be utilized withany electrically controlled recording or reading device in addition tothe printer described for the preferred embodiment. Further, while thetracks for the preferred embodiment have been optical sync tracks whichare optically read, it is apparent that the teachings of this inventioncould be applied with magnetic or other sync tracks. Thus, While theinvention has been particularly shown and described above with referenceto preferred embodiments, it will be apparent to those skilled in theart that the foregoing and other changes in form and detail may be madetherein without departing from the spirit and scope of the invention.

What is claimed is:

1. In an electrically controlled recording device for recording a lineof characters on a recording medium,

a recording head movable along a line relative to said medium andoperable in response to enabling synchronization signals applied theretofor producing selected strokes along said lines so that each characteron the line is formed from a plurality of said strokes,

a synchronization track having spaced synchronization marks located in afixed position relative to said recording medium, and

detecting means for detecting said synchronization marks during relativemovement of said head and said medium for producing a synchronizationsignal in response to each detected mark, each synchronization signalbeing controllingly coupled to said recording head for enabling saidhead to produce a stroke at a location along said line corresponding tothe location of said head when the synchronization signal is produced,

said synchronization marks being spaced on said track so that thestrokes produced by said recording head for a character at a firstlocation along said line will be spaced differently from those producedby said recording head for a character at a second location along saidline.

2. The invention in accordance with claim 1, wherein synchronizationmarks are provided on said track only at locations at which it isdesired that a stroke be produced by said recording head.

3. The invention in accordance with claim 1, wherein the recording headproduces visual strokes on said medium, and wherein the synchronizationmarks corresponding to the character at said second location are spacedcloser together than the synchronization marks corresponding to thecharacter at said first location so as to thereby cause said recordingmeans to produce characters having different recording densities.

4. The invention in accordance with claim 1, wherein the recording headis adapted to produce non-visual strokes, and wherein thesynchronization marks provided on said track corresponding to at leastone charactcr are located so that the recording head will producedifferent spacings between the strokes of the character, therebyproviding for recording of a character in coded form.

5. The invention in accordance with claim 1. wherein said recording headmoves more slowly during acceleration and deceleration than when movingat normal speed, and wherein the synchronization marks provided at thebeginning and end of said track are spaced closer together than those atthe center of the track in order to compensate for the slower speed ofthe recording head during acceleration and deceleration.

6. In a high speed electrically controlled recording device forrecording a line of characters on a recording medium,

a recording head movable in either direction along a line relative tosaid medium and operable in response to enabling synchronization signalsapplied thereto during continuous movement of the head in eitherdirection for producing selected strokes along said line so that eachcharacter on the line is formed from a predetermined plurality of saidstrokes,

a synchronization track having spaced synchronization marks located in afixed position relative to said recording medium and,

detecting means for detecting said synchronization marks during relativemovement of said head and said medium and for producing asynchronization signal in response to each detected mark, eachsynchronization signal being applied to said recording head forproducing a stroke at a location along said line corresponding to thelocation of said head when the synchronization signal is produced,

said detecting means being responsive to the leading edge of eachsynchronization mark during relative movement of said head in eitherdirection, and said synchronization marks having a width chosen inconjunction with the speed of relative movement of said head so thateach stroke will be recorded at its proper position along a lineregardless of the direction of movement of the recording head.

7. In an electrically controlled recording device for recording a lineof characters on a recording medium,

a recording head movable along a line relative to said medium andoperable in response to enabling synchronizing signals applied theretofor producing selected strokes along said line so that each character onthe line is formed from a predetermined plurality of said strokes,

a synchronization track having spaced synchronization marks located in afixed position relative to said recording medium and,

detecting means coupled to said recording head for detecting saidsynchronization marks during relative movement of said head and saidmedium and for producing a synchronization signal in response to eachdetected mark, each synchronization signal being applied to saidrecording head for producing a stroke at a location along said linecorresponding to the location of said head when the synchronizationsignal is produced,

a shutter relatively movable with respect to said track for preventing aselected plurality of said synchronization marks from being detected bysaid detecting means, and

8. The invention in accordance with claim 7, wherein said predeterminedperiod of time is at least three synchronization signal intervals.

1. In an electrically controlled recording device for recording a lineof characters on a recording medium, a recording head movable along aline relative to said medium and operable in response to enablingsynchronization signals applied thereto for producing selected strokesalong said lines so that each character on the line is formed from aplurality of said strokes, a synchronization track having spacedsynchronization marks located in a fixed position relative to saidrecording medium, and detecting means for detecting said synchronizationmarks during relative movement of said head and said medium forproducing a synchronization signal in response to each detected mark,each synchronization signal being controllingly coupled to saidrecording head for enabling said head to produce a stroke at a locationalong said line corresponding to the location of said head when thesynchronization signal is produced, said synchronization marks beingspaced on said track so that the strokes produced by said recording headfor a character at a first location along said line will be spaceddifferently from those produced by said recording head for a characterat a second location along said line.
 2. The invention in accordancewith claim 1, wherein synchronization marks are provided on said trackonly at locations at which it is desired that a stroke be produced bysaid recording head.
 3. The invention in accordance with claim 1,wherein the recording head produces visual strokes on said medium, andwherein the synchronization marks corresponding to the character at saidsecond location are spaced closer together than the synchronizationmarks corresponding to the character at said first location so as tothereby cause said recording means to produce characters havingdifferent recording densities.
 4. The invention in accordance with claim1, wherein the recording head is adapted to produce non-visual strokes,and wherein the synchronization marks provided on said trackcorresponding to at least one character are located so that therecording head will produce different spacings between the strokes ofthe character, thereby providing for recording of a character in codedform.
 5. The invention in accordance with claim 1, wherein saidrecording head moves more slowly during acceleration and decelerationthan when moving at normal speed, and wherein the synchronization marksprovided at the beginning and end of said track are spaced closertogether than those at the center of the track in order to compensatefor the slower speed of the recording head during acceleration anddeceleration.
 6. In a high speed electrically controlled recordingdevice for recording a line of characters on a recording medium, arecording head movable in either direction along a line relative to saidmedium and operable in response to enabling synchronization signalsapplied thereto during continuous movement of the head in eitherdirection for producing selected strokes along said line so that eachcharacter on the line is formed from a predetermined plurality of saidstrokes, a synchronization track having spaced synchronization markslocated in a fixed position relative to said recording medium and,detecting means for detecting said synchronization marks during relativemovement of said head and said medium and for producing asynchronization signal in response to each detected mark, eachsynchronization signal being applied to said recording head forproducing a stroke at a location along said line corresponding to thelocation of said head when the synchronization signal is produced, saiddetecting means being responsive to the leading edge of eachsynchronization mark during relative movement of said head in eitherdirection, and said synchronization marks having a width chosen inconjunction with the speed of relative movement of said head so thateach stroke will be recorded at its proper position along a lineregardless of the direction of movement of the recording head.
 7. In anelectrically controlled recording device for recording a line ofcharacters on a recording medium, a recording head movable along a linerelative to said medium and operable in response to enablingsynchronizing signals applied thereto for producing selected strokesalong said line so that each character on the line is formed from apredetermined plurality of said strokes, a synchronization track havingspaced synchronization marks located in a fixed position relative tosaid recording medium and, detecting means coupled to said recordinghead for detecting said synchronization marks during relative movementof said head and said medium and for producing a synchronization signalin response to each detected mark, each synchronization signal beingapplied to said recording head for producing a stroke at a locationalong said line corresponding to the location of said head when thesynchronization signal is produced, a shutter relatively movable withrespect to said track for preventing a selected plurality of saidsynchronization marks from being detected by said detecting means, andelectrical circuit means to which said synchronization signals areapplied for producing an output signal when a Synchronization signal isnot received within a predetermined period of time from a previouslyreceived synchronization signal.
 8. The invention in accordance withclaim 7, wherein said predetermined period of time is at least threesynchronization signal intervals.